Protocol for cooperation communication between access points in overlapped basic service set (OBSS) environment

ABSTRACT

Disclosed is a protocol for transmitting data through cooperation between access points in an overlapped basic service set (OBSS) environment. A cooperative beamforming communication method may include negotiating, by a first access point, a cooperative transmit beamforming with a second access point having an OBSS area with the first access point; transmitting, by the first access point, a clear-to-send (CTS) to the second access point; and performing, by the first access point, the cooperative transmit beamforming with the second access point during a cooperative transmit beamforming duration determined through the negotiation after a predetermined time interval is elapsed, when transmission of the CTS is completed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/681,425, filed Apr. 8, 2015, now U.S. Pat. No. 9,602,174 B2, whichclaims the priority benefit of Korean Patent Application No.10-2014-0041808, filed on Apr. 8, 2014, Korean Patent Application No.10-2014-0041809, filed on Apr. 8, 2014, Korean Patent Application No.10-2015-0048169, filed on Apr. 6, 2015, and Korean Patent ApplicationNo. 10-2015-0048170, filed on Apr. 6, 2015, in the Korean IntellectualProperty Office, the disclosures of which are incorporated herein byreference.

BACKGROUND

1. Field of the Invention

Embodiments of the present invention relate to a media access control(MAC) protocol of a wireless local area network (WLAN), and moreparticularly, to a protocol for transmitting data through cooperationbetween access points (APs) in an overlapped basic service set (OBSS)environment.

2. Description of the Related Art Currently, multiple input multipleoutput (MIMO) communication technology for transmitting and receivingdata using two or more antennas has been generalized in a wirelesscommunication system. Further, according to standards starting from anInstitute of Electrical and Electronics Engineers (IEEE) 802.11nstandard, a wireless local area network (WLAN) allows two or moretransmit antennas to be available. According to the IEEE 802.11nstandard, up to four transmit antennas may be used. According to an IEEE802.11ac standard, up to eight transmit antennas may be used. Inaddition, when using a plurality of transmit antennas, data may betransmitted using a transmit beamforming technology to improve thesignal reception performance. The IEEE 802.11ac standard includes adownlink multi-user (MU) MIMO technology that enables an access point(AP) to concurrently transmit beamformed data frames to a plurality ofstations (STAs).

However, according to a recent increase in the complexity of a WLANenvironment, an overlapped basic service set (OBSS) frequently appears.Here, the OBSS indicates an overlapping area between a BSS correspondingto a service area covered by a single AP and a BSS covered by anotherAP. In an OBSS environment, the transmission efficiency may be degradedand thus, a method for performing an efficient transmission even in theOBSS environment is required.

SUMMARY

According to an aspect, there is provided a cooperative beamformingcommunication method including negotiating, by a first access point, acooperative transmit beamforming with a second access point having anoverlapped basic service set (OBSS) area with the first access point;transmitting, by the first access point, a clear-to-send (CTS) to thesecond access point; and performing, by the first access point, thecooperative transmit beamforming with the second access point during acooperative transmit beamforming duration determined through thenegotiation after a predetermined time interval is elapsed, whentransmission of the CTS is completed.

The cooperative beamforming communication method may further includeperforming, by the first access point, cooperative sounding with thesecond access point. The performing of the cooperative sounding mayinclude acquiring, by the first access point, a precoding matrix to beused for the cooperative transmit beamforming.

A duration field of the CTS may be set as a time when the cooperativetransmit beamforming duration is terminated.

The predetermined time interval may be a short inter-frame space (SIFS).

The performing of the cooperative transmit beamforming may includetransmitting, by the first access point, a first beamformed data frameto a first station positioned in the OBSS area; and transmitting, by thesecond access point, a second beamformed data frame to a second stationpositioned in the OBSS area.

According to another aspect, there is provided a cooperative beamformingcommunication method including negotiating, by a first access point, acooperative transmit beamforming with a second access point having anBSS area with the first access point; resetting, by the first accesspoint, a network allocation vector (NAV) of the first access point inresponse to a CTS associated with the negotiation received from thesecond access point; and performing, by the first access point, thecooperative transmit beamforming with the second access point during acooperative transmit beamforming duration determined through thenegotiation after a predetermined time interval is elapsed, whenreception of the CTS is completed.

The cooperative beamforming communication method may further includeperforming, by the first access point, cooperative sounding with thesecond access point. The performing of the cooperative sounding mayinclude acquiring, by the first access point, a precoding matrix to beused for the cooperative transmit beamforming.

A duration field of the CTS may be set as a time when the cooperativetransmit beamforming duration is terminated.

The predetermined time interval may be a SIFS.

The performing of the cooperative transmit beamforming may includetransmitting, by the first access point, a first beamformed data frameto a first station positioned in the OBSS area; and transmitting, by thesecond access point, a second beamformed data frame to a second stationpositioned in the OBSS area.

According to still another aspect, there is provided a cooperativebeamforming communication method including negotiating a cooperativetransmit beamforming between a plurality of access points having an OBSSarea; transmitting, by at least one of the access points, a CTS to oneor more other access points among the access points; resetting, by theone or more other access points, a NAV of the one or more other accesspoints in response to the CTS; and performing, by the plurality ofaccess points, the cooperative transmit beamforming during a cooperativetransmit beamforming duration determined through the negotiation.

The cooperative beamforming communication method may further includeperforming cooperative sounding between the plurality of access points.The performing of the cooperative sounding may include acquiring, byeach of the plurality of access points, a precoding matrix to be usedfor the cooperative transmit beamforming. A duration field of the CTSmay be set as a time when the cooperative transmit beamforming durationis terminated.

The performing of the cooperative transmit beamforming may includetransmitting, by the one or more access points, a first beamformed dataframe after a predetermined time interval is elapsed, when transmissionof the CTS is completed; and transmitting, by the one or more otheraccess points, a second beamformed data frame after a predetermined timeinterval is elapsed, when reception of the CTS is completed. Thepredetermined time interval may be a SIFS.

According to still another aspect, there is provided an access point toperform cooperative beamforming communication, the access pointincluding a communicator configured to transmit and receive a frameassociated with negotiation about a cooperative transmit beamformingwith one or more other access points having an OBSS area with the accesspoint, to transmit a CTS to the one or more other access points, and toperform the cooperative transmit beamforming with the one or more otheraccess points; and a controller configured to control the communicatorto generate a frame associated with the negotiation and to transmit thegenerated frame to the one or more other access points, to control thecommunicator to process the frame associated with the negotiation andtransmit a CTS to the one or more other access points in response to theframe associated with the negotiation received from the other accesspoint to the communicator, and to control the communicator to performthe cooperative transmit beamforming with the one or more other accesspoints during a cooperative transmit beamforming duration determinedthrough the negotiation after a predetermined time interval is elapsed,when transmission of the CTS is completed.

The controller may also control the communicator to perform cooperativesounding with the one or more other access points. The performing of thecooperative sounding may include acquiring, by the access point, aprecoding matrix to be used for the cooperative transmit beamforming.

A duration field of the CTS may be set as a time when the cooperativetransmit beamforming duration is terminated.

The predetermined time interval may be a SIFS.

According to still another aspect, there is provided an access point toperform cooperative beamforming communication, the access pointincluding a communicator configured to transmit and receive a frameassociated with negotiation about a cooperative transmit beamformingwith one or more other access points having an OBSS area with the accesspoint, to receive a CTS from the one or more other access points, and toperform the cooperative transmit beamforming with the one or more otheraccess points; and a controller configured to control the communicatorto generate a frame associated with the negotiation and to transmit thegenerated frame to the one or more other access points, and to controlthe communicator to process the frame associated with the negotiation inresponse to the frame associated with the negotiation received the oneor more other access points to the communicator, to reset a NAV inresponse to the CTS received by the communicator from the other accesspoint, to reset a NAV in response to the CTS received by thecommunicator from the one or more other access points, and to performthe cooperative transmit beamforming with the one or more other accesspoints during a cooperative transmit beamforming duration determinedthrough the negotiation after a predetermined time interval is elapsed,when reception of the CTS is completed.

The controller may also control the communicator to perform cooperativesounding with the one or more other access points. The performing of thecooperative sounding may include acquiring, by the access point, aprecoding matrix to be used for the cooperative transmit beamforming.

A duration field of the CTS may be set as a time when the cooperativetransmit beamforming duration is terminated.

The predetermined time interval may be a SIFS.

According to still another aspect, there is provided a cooperativebeamforming communication method including negotiating, by a firstaccess point, a cooperative transmit beamforming with a second accesspoint having an OBSS area with the first access point; transmitting, bythe first access point, a cooperative transmission request frame to thesecond access point; receiving, by the first access point, a cooperativetransmission response frame that is transmitted from the second accesspoint to the first access point in response to the cooperativetransmission request frame; and performing, by the first access point,the cooperative transmit beamforming with the second access point duringa cooperative transmit beamforming duration determined through thenegotiation after a predetermined time interval is elapsed, whenreception of the cooperative transmission response frame is completed.

The cooperative beamforming communication method may further includeperforming, by the first access point, cooperative sounding with thesecond access point. The performing of the cooperative sounding mayinclude acquiring, by each of the first access point and the secondaccess point, a precoding matrix to be used for the cooperative transmitbeamforming.

A duration field of the cooperative transmission request frame and aduration field of the cooperative transmission response frame may be setas a time when the cooperative transmit beamforming duration isterminated.

The predetermined time interval may be a SIFS.

According to still another aspect, there is provided a cooperativebeamforming communication method including negotiating, by a firstaccess point, a cooperative transmit beamforming with one or more accesspoints having an OBSS area with the first access point; broadcasting, bythe first access point, a cooperative transmission request frame;receiving, by the first access point, a cooperative transmissionresponse frame that is transmitted from the one or more access points tothe first access point in response to the cooperative transmissionrequest frame; and performing, by the first access point, thecooperative transmit beamforming with the one or more access pointsduring a cooperative transmit beamforming duration determined throughthe negotiation after a predetermined time interval is elapsed, whenreception of the cooperative transmission response frame is completed.

The one or more access points may include a second access point and athird access point. The receiving of the cooperative transmissionresponse frame may include receiving a first cooperative transmissionresponse frame transmitted from the second access point to the firstaccess point; and receiving a second cooperative transmission responseframe transmitted from the third access point to the first access pointafter the second access point transmits the first cooperativetransmission response frame to the first access point. Here, thecooperative beamforming communication method may further includetransmitting, by the first access point, a cooperative transmissionstart frame. The performing of the cooperative transmit beamforming mayinclude transmitting, by each of the first access point, the secondaccess point, and the third access point, a beamformed data frame whentransmission of the cooperative transmission start frame is completed.

The one or more access points may include a second access point and athird access point. The receiving of the cooperative transmissionresponse frame may include receiving a first cooperative transmissionresponse frame transmitted from the second access point to the firstaccess point; transmitting, by the first access point, a cooperativetransmission response poll frame to the third access point in responseto the first cooperative transmission response frame transmitted fromthe second access point to the first access point; and receiving asecond cooperative transmission response frame transmitted from thethird access point to the first access point in response to thecooperative transmission response poll frame. Here, the performing ofthe cooperative transmit beamforming includes transmitting, by each ofthe first access point, the second access point, and the third accesspoint, a beamformed data frame when reception of the second cooperativetransmission response frame is completed.

The cooperative beamforming cooperation method may further includeperforming cooperative sounding between the first access point and theone or more access points. The performing of the cooperative soundingmay include acquiring, by each of the first access point and the one ormore access points, a precoding matrix to be used for the cooperativetransmit beamforming.

A duration field of the cooperative transmission request frame and aduration field of the cooperative transmission response frame may be setas a time when the cooperative transmit beamforming duration isterminated.

According to still another aspect, there is provided an access point toperform cooperative beamforming communication, the access pointincluding a communicator configured to transmit and receive a frameassociated with negotiation about a cooperative transmit beamformingwith one or more other access points having an OBSS area with the accesspoint, to transmit a cooperative transmission request frame to the oneor more other access points, and to receive a cooperative transmissionresponse frame that is transmitted from the one or more other accesspoints in response to the cooperative transmission request frame; and acontroller configured to control the communicator to generate a frameassociated with the negotiation and to transmit the generated frame tothe one or more other access points, and to control the communicator toprocess the frame associated with the negotiation in response to theframe associated with the negotiation received by the communicator fromthe one or more other access points, to generate the cooperativetransmission request frame to be transmitted to the one or more otheraccess points, and to perform the cooperative transmit beamforming withthe one or more other access points during a cooperative transmitbeamforming duration determined through the negotiation after apredetermined time interval is elapsed, when reception of thecooperative transmission response frame is completed.

The controller may also control the communicator to perform cooperativesounding with the one or more other access points. The performing of thecooperative sounding may include acquiring, by the access point, aprecoding matrix to be used for the cooperative transmit beamforming.

A duration field of the cooperative transmission request frame and aduration field of the cooperative transmission response frame may be setas a time when the cooperative transmit beamforming duration isterminated.

The predetermined time interval may be a SIFS.

According to still another aspect, there is provided an access point toperform cooperative beamforming communication, the access pointincluding a communicator configured to transmit and receive a frameassociated with negotiation about a cooperative transmit beamformingwith one or more other access points having an OBSS area with the accesspoint, to broadcast a cooperative transmission request frame, and toreceive a cooperative transmission response frame that is transmittedfrom the one or more access points to the first access point in responseto the cooperative transmission request frame; and a controllerconfigured to control the communicator to generate a frame associatedwith the negotiation and to transmit the generated frame to the one ormore other access points, and to control the communicator to process theframe associated with the negotiation in response to the frameassociated with the negotiation received by the communicator from theone or more other access points, to generate the cooperativetransmission request frame, and to perform the cooperative transmitbeamforming with the one or more access points during a cooperativetransmit beamforming duration determined through the negotiation, whenreception of the cooperative transmission response frame is completed.

The one or more access points may include a second access point and athird access point. The communicator may also receive a firstcooperative transmission response frame transmitted from the secondaccess point, and may receive a second cooperative transmission responseframe transmitted from the third access point after the second accesspoint transmits the first cooperative transmission response frame.

The communicator may also transmit a cooperative transmission startframe. Also, the controller may control the communicator to transmit abeamformed data frame when transmission of the cooperative transmissionstart frame is completed.

The one or more access points may include a second access point and athird access point. The communicator may receive a first cooperativetransmission response frame transmitted from the second access point,may transmit a cooperative transmission response poll frame to the thirdaccess point in response to the first cooperative transmission responseframe, and may receive a second cooperative transmission response frametransmitted from the third access point in response to the cooperativetransmission response poll frame. Also, the controller may control thecommunicator to transmit a beamformed data frame when reception of thesecond cooperative transmission response frame is completed.

The controller may control the communicator to perform cooperativesounding with the one or more access points. The performing of thecooperative sounding may include acquiring, by the access point, aprecoding matrix to be used for the cooperative transmit beamforming.

A duration field of the cooperative transmission request frame and aduration field of the cooperative transmission response frame may be setas a time when the cooperative transmit beamforming duration isterminated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects, features, and advantages of the inventionwill become apparent and more readily appreciated from the followingdescription of exemplary embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 illustrates an environment in which basic service sets (BSSs)covered by access points (APs) of a wireless local area network (WLAN)overlap;

FIG. 2 illustrates a situation in which the transmission efficiencydegrades in an environment in which BSSs covered by APs of a WLANoverlap according to the related art;

FIG. 3 is a flowchart illustrating a method of performing cooperativetransmit beamforming between APs according to an embodiment;

FIG. 4 illustrates an example of a protocol for performing cooperativetransmit beamforming between APs according to an embodiment;

FIG. 5 illustrates another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment;

FIG. 6 illustrates a format of a cooperative transmission (CoTx) requestframe according to an embodiment;

FIG. 7 illustrates an environment in which BSSs covered by APs of a WLANoverlap;

FIG. 8 illustrates another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment;

FIG. 9 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment;

FIG. 10 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment;

FIG. 11 illustrates an example in which BSSs covered by APs of a WLANoverlap; and

FIG. 12 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout. Exemplary embodiments are described below to explain thepresent invention by referring to the figures.

The terms used herein may be most widely used general terms that areselected based on functions in the proposed disclosure. However, theterms may be modified based on the intent or custom of those skilled inthe art or the appearance of new art.

Also, in some cases, some terms may be arbitrarily used by the applicantto help the understanding and/or for convenience of description. In thisexample, the detailed meaning thereof will be described in acorresponding description portion. Accordingly, the terms used in thefollowing description should be understood based on meanings of theterms and the overall description of the specification.

FIG. 1 illustrates an environment in which basic service sets (BSSs)covered by access points (APs) of a wireless local area network (WLAN)overlap.

Referring to FIG. 1, a BSS 121 is covered by an AP 111 and a BSS 122 iscovered by an AP 112. Stations (STAs) 131 and 133 may belong to the BSS121, and STAs 132 and 134 may belong to the BSS 122. An overlapping areamay be present between the BSSs 121 and 122 of the APs 111 and 112. TheSTA 131 belonging to the BSS 121 and the STA 132 belonging to the BSS122 may be positioned in the overlapping area. Here, when the BSSs 121and 122 use the same frequency channel, the APs 111 and 112 and the STAs131 and 132 may hear all of the transmitting frames. Accordingly, thetransmission efficiency may be degraded in the overlapping area. Asituation in which the degradation in the transmission efficiency occurswill be further described with reference to FIG. 2.

An AP according to an embodiment may include a controller and acommunicator. The controller may generate a frame to be transmitted fromthe communicator, and the controller may also process a frame receivedby the communicator. The controller may control the communicator tocommunicate with a communicator with an STA using a multiple inputmultiple output (MIMO) communication method, and may determine an STA toperform communication through the communicator. The controller may beembodied using an integrated circuit (IC) chip, a microprocessor, and amini computer. The communicator of the AP may communicate with acommunicator with another AP or the communicator of the STA. Thecommunicator may include a variety of communication modules such as anantenna, a modulator/demodulator, a frequency processing apparatus, anda filtering apparatus.

FIG. 2 illustrates a situation in which the transmission efficiencydegraded in an environment in which BSSs covered by APs of a WLANoverlap according to the related art.

Referring to FIG. 2, in an example in which an overlapped BSS (OBSS)area is present between AP1 and AP2, and STA1 and STA2 are present inthe OBSS area, when AP1 transmits a frame, channels of AP2 and STA2 arein a busy state. Similarly, when STA1 transmits a frame, the channels ofAP2 and STA2 are in a busy state. Also, when AP2 transmits a frame,channels of AP1 and STA1 are in a busy state. Similarly, when STA2transmits a frame, the channels of AP1 and STA1 are in a busy state.That is, compared to an environment in which an OBSS is absent, a busystate in which a transmission is impossible increases, which may lead todegrading the transmission efficiency. In particular, when a durationfield of a frame transmitted from a neighboring BSS is not zero, anetwork allocation vector (NAV) is set as a value of the duration fieldand thus, the busy state in which the transmission is impossible maycontinue until the NAV is terminated, thereby degrading the transmissionefficiency. Accordingly, there is a need for a method of preventing thetransmission efficiency from being degraded in an OBSS environment.Proposed herein is a method that enables two or more APs to concurrentlytransmit data even in the OBSS environment, thereby enhancing thetransmission efficiency in the OBSS environment.

FIG. 3 is a flowchart illustrating a method of performing cooperativetransmit beamforming between APs according to an embodiment.

In operation 310, a negotiation about a cooperative transmit beamformingmay be performed between neighboring APs having an OBSS area. Throughthe negotiation, APs to participate in the cooperative transmitbeamforming and a cooperative transmit beamforming duration may bedetermined. According to an embodiment, a leading AP to lead thecooperative transmit beamforming may be determined among the APsdetermined to participate in the cooperative transmit beamforming,through the negotiation. Operation 310 may be performed through wired orwireless communication between the APs.

In operation 320, a cooperative sounding process for the cooperativetransmit beamforming between the APs associated with the negotiation,that is, the APs to participate in the cooperative transmit beamformingmay be performed. The cooperative sounding process may include a processof acquiring channel information between a terminal, that is, abeamformer to perform transmission and a terminal, that is, a beamformeeto perform reception in the cooperative transmit beamforming. Accordingto an embodiment, the cooperative sounding process may include anoperation of acquiring a precoding matrix to be used for the cooperativetransmit beamforming. The precoding matrix may be configured toeliminate or minimize interference during the cooperative transmitbeamforming. Operation 320 may be performed through wired or wirelesscommunication between the APs.

In operation 330, NAVs of APs associated with the negotiation may bereset and NAVs of WLAN equipments unassociated with the negotiation maybe set. That is, a protection may be performed to enable thetransmission during the cooperative transmit beamforming duration byresetting the NAVs of the APs participating in the cooperative transmitbeamforming, and to disable the transmission during the cooperativetransmit beamforming duration by setting the NAVs of the WLAN equipmentsthat do not participate in the cooperative transmit beamforming.

According to an embodiment, an AP leading a cooperative transmitbeamforming among APs participating in the cooperative transmitbeamforming may transmit a clear-to-send (CTS) in which an APparticipating in cooperative transmit beamforming is set as a receiveraddress (RA). According to an Institute of Electrical and ElectronicsEngineers (IEEE) 802.11 standard, a WLAN equipment receiving a CTS inwhich the WLAN equipment is set as a receiver address may reset a NAV,and a WLAN equipment receiving a CTS in which the WLAN equipment is notset as a receiver address may set a NAV based on a value set in aduration field of the CTS. Accordingly, when the AP leading thecooperative transmit beamforming transmits a CTS in which an APparticipating in the cooperative transmit beamforming is set as areceiver address and a duration field is set as a time when thecooperative transmit beamforming duration is terminated, the APparticipating in the cooperative transmit beamforming may reset a NAVand a WLAN equipment that does not participate in the cooperativetransmit beamforming may set a NAV until the cooperative transmitbeamforming duration is terminated.

According to another embodiment, an AP leading a cooperative transmitbeamforming among APs participating in the cooperative transmitbeamforming may transmit a cooperative transmission (CoTx) request framein which an AP participating in the cooperative transmit beamforming isset as a receiver address. When the AP leading the cooperative transmitbeamforming transmits a CoTx request frame in which an AP participatingin the cooperative transmit beamforming is set as a receiver address anda duration field is set as a time when a cooperative transmitbeamforming duration is terminated, the AP participating in thecooperative transmit beamforming may reset a NAV and a WLAN equipmentthat does not participate in the cooperative transmit beamforming mayset a NAV until the cooperative transmit beamforming duration isterminated.

Accordingly, the APs associated with the negotiation may concurrentlyperform the cooperative transmit beamforming, and the WLAN equipmentsunassociated with the negotiation may not transmit a frame during thecooperative transmit beamforming duration.

In operation 340, the APs associated with the negotiation may performthe cooperative transmit beamforming during the cooperative transmitbeamforming duration. Each of the APs associated with the negotiationmay transmit beamformed data to an STA included in a BSS covered by acorresponding AP. For example, when AP1 and AP2 are associated with anegotiation, AP1 may transmit a beamformed data frame to STA1 and an AP2may transmit a beamformed data frame to STA2. The beamformed data framesmay be concurrently transmitted from AP1 and AP2 during the cooperativetransmit beamforming duration. According to an embodiment, atransmission of a beamformed data frame may be performed using adownlink MU-MIMO technology.

As described above, according to embodiments, the transmissionefficiency in an OBSS environment may be enhanced by providing acooperative transmit beamforming method that enables two or more APs toconcurrently perform a transmit beamforming in the OBSS environment.

FIG. 4 illustrates an example of a protocol for performing cooperativetransmit beamforming between APs according to an embodiment.

Referring to FIG. 4, AP1 and AP2 may be determined to participate incooperative transmit beamforming through negotiation about thecooperative transmit beamforming. Here, a cooperative sounding processfor the cooperative transmit beamforming between AP1 and AP2 may beperformed. For example, each of AP1 and AP2 may acquire a precodingmatrix to be used for the cooperative transmit beamforming through thecooperative sounding process. AP1 leading the cooperative transmitbeamforming may transmit a CTS in which AP2 is set as a receiver address(RA), so that AP2 may reset a NAV. Here, a duration field of the CTS isset as a time when the cooperative transmit beamforming duration isterminated and thus, a WLAN equipment unassociated with the negotiationmay set a NAV until the cooperative transmit beamforming duration isterminated. AP1 and AP2 may concurrently perform the cooperativetransmit beamforming during the cooperative transmit beamformingduration. For example, AP1 may transmit a beamformed data frame to STA1belonging to a BSS covered by AP1 and, at the same time, AP2 maytransmit a beamformed data frame to STA2 belonging to a BSS covered byAP2. According to an embodiment, AP1 may transmit a beamformed dataframe to STA1 after a predetermined time interval is elapsed, whentransmission of a CTS is completed. AP2 may transmit a beamformed dataframe to STA2 after a predetermined time interval is elapsed whenreception of the CTS is completed. Here, the predetermined time intervalmay be a short inter-frame space (SIFS).

FIG. 5 illustrates another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.

Referring to FIG. 5, AP1 and AP2 may be determined to participate in acooperative transmit beamforming through negotiation about thecooperative transmit beamforming. Here, a cooperative sounding processfor the cooperative transmit beamforming between AP1 and AP2 may beperformed. For example, each of AP1 and AP2 may acquire a precodingmatrix to be used for the cooperative transmit beamforming through thecooperative sounding process. AP1 leading the cooperative transmitbeamforming may transmit a CoTx request frame in which AP2 is set as areceiver address (RA), so that AP2 may reset a NAV. Here, a durationfield of the CoTx request frame may be set as a time when a cooperativetransmit beamforming duration is terminated and thus, a WLAN equipmentunassociated with the negotiation may set a NAV until the cooperativetransmit beamforming duration is terminated. AP2 receiving the CoTxrequest frame may transfer an acknowledgement (ACK) frame about the CoTxrequest frame to AP1 by transmitting a CoTx response frame in which AP1is set as a receiver address. Here, a duration field of the CoTxresponse frame is set as a time when the cooperative transmitbeamforming duration is terminated and a WLAN equipment unassociatedwith the negotiation may set a NAV until the cooperative transmitbeamforming duration is terminated. Here, AP1 and AP2 may concurrentlyperform the cooperative transmit beamforming during the cooperativetransmit beamforming duration. For example, AP1 may transmit abeamformed data frame to STA1 belonging to a BSS covered by AP1 and, atthe same time, AP2 may transmit a beamformed data frame to STA2belonging to a BSS covered by AP2. According to an embodiment, AP1 maytransmit a beamformed data frame to STA1 after a predetermined timeinterval is elapsed, when reception of a CoTx response frame iscompleted. AP2 may transmit a beamformed data frame to STA2 after apredetermined time interval is elapsed, when transmission of the CoTxresponse frame is completed. Here, the predetermined time interval maybe a SIFS.

As described above, according to embodiments, the transmissionefficiency in an OBSS environment may be enhanced by providing acooperative transmit beamforming method that enables two or more APs toconcurrently perform a transmit beamforming in the OBSS environment.

FIG. 6 illustrates a format of a CoTx request frame according to anembodiment.

The CoTx request frame may include a frame control (FC) field, aduration field, a receiver address (RA) field, a transmitter address(TA) field, and a frame check sequence (FCS) field as basic fields thatconstitute a WLAN MAC frame. According to an embodiment, the CoTxrequest frame may include a CoTx control field and a plurality of CoTxAP info fields to perform a cooperative transmit beamforming. The CoTxcontrol field may include information about the number of APsparticipating in the cooperative transmit beamforming and information,for example, information constituting L-LENGTH and VHT-SIGA in the caseof VHT PPDU, used to make a temporal length of a beamformed data frameequal to a temporal length of a un-beamformed data frame, for example,L-SIG and VHT-SIGA in the case of VHT PPDU. The number of CoTx AP infofields may be the same as the number of APs participating in thecooperative transmit beamforming. The CoTx AP info fields may includeinformation indicating the APs that participate in the cooperativetransmit beamforming, respectively. Information indicating each of theAPs that participate in the cooperative transmit beamforming may includea BSS ID or information capable of identifying a corresponding AP.

FIG. 7 illustrates an environment in which BSSs covered by APs of a WLANoverlap.

Referring to FIG. 7, a BSS 121 is covered by an AP 111, a BSS 122 iscovered by an AP 112, and a BSS 123 is covered by an AP 113. STAs 131and 134 may belong to the BSS 121, STAs 132 and 135 may belong to theBSS 122, and STAs 133 and 136 belong to the BSS 123. An overlapping areamay be present among the BSSs 121, 122, and 123 of the APs 111, 112, and113. The STA 131 belonging to the BSS 121, the STA 132 belonging to theBSS 122, and the STA 133 belonging to the BSS 123 may be positioned inthe overlapping area. Here, when the BSSs 121, 122, and 123 use the samefrequency channel, the APs 111, 112, and 123 and the STAs 131, 132, and133 may hear all of the transmitting frames. Accordingly, thetransmission efficiency may be degraded in the overlapping area. Amethod of preventing the degradation in the transmission efficiency inan OBSS environment is required.

According to embodiments, the transmission efficiency in an OBSSenvironment may be enhanced by providing a method that enables three ormore APs to concurrently transmit data even in the OBSS environment.

FIG. 8 illustrates another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.In FIG. 8, APs participating in the cooperative transmit beamformingsequentially respond to a single CoTx request frame.

Referring to FIG. 8, AP1, AP2, and AP3 may be determined to participatein the cooperative transmit beamforming through negotiation about thecooperative transmit beamforming. A cooperative sounding process for thecooperative transmit beamforming among AP1, AP2, and AP3 may beperformed. For example, each of AP1, AP2, and AP3 may acquire aprecoding matrix to be used for the cooperative transmit beamformingthrough the cooperative sounding process. AP1 leading the cooperativetransmit beamforming may transmit a CoTx request frame in which abroadcast address (BC) is set as a receiver address. Here, a durationfield of the CoTx request frame is set as a time when a cooperativetransmit beamforming duration is terminated and thus, a WLAN equipmentunassociated with the negotiation may set a NAV until the cooperativetransmit beamforming duration is terminated. Also, a first CoTx AP infofield of the CoTx request frame may include information indicating AP2and a second CoTx AP info field of the CoTx request frame may includeinformation indicating AP3. Accordingly, AP2 and AP3 participating inthe cooperative transmit beamforming may rest a NAV. AP2 associated withthe first CoTx AP info field may transfer an ACK frame about the CoTxrequest frame to AP1 by transmitting a CoTx response frame in which AP1is set as a receiver address. Here, a duration field of the CoTxresponse frame is set as a time when the cooperative transmitbeamforming duration is terminated and thus, the WLAN equipmentunassociated with the negotiation may set a NAV until the cooperativetransmit beamforming duration is terminated. AP3 associated with asubsequent CoTx AP info field may transfer an ACK frame about the CoTxrequest frame to AP1 by transmitting a CoTx response frame in which AP1is set as a receiver address. Here, a duration field of the CoTxresponse frame is set as a time when the cooperative transmitbeamforming duration is terminated and thus, the WLAN equipmentunassociated with the negotiation may set a NAV until the cooperativetransmit beamforming duration is terminated. AP1, AP2, and AP3 mayperform the cooperative transmit beamforming during the cooperativetransmit beamforming duration. For example, AP1 may transmit abeamformed data frame to STA1 belonging to a BSS covered by AP1, AP2, atthe same time, may transmit a beamformed data frame to STA2 belonging toa BSS covered by AP2, and AP3, at the same time, may transmit abeamformed data frame to STA3 belonging to a BSS covered by AP3.According to an embodiment, AP1 and AP2 may transmit beamformed dataframes to STA1 and STA2, respectively after a predetermined timeinterval is elapsed, when reception of a last CoTx response frame iscompleted. AP3 associated with a last CoTx AP info field may transmit abeamformed data frame to STA3 after a predetermined time interval iselapsed, when transmission of a CoTx response frame is completed. Here,the predetermined time interval may be a SIFS.

FIG. 9 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.In FIG. 9, APs participating in the cooperative transmit beamformingsequentially respond to a single CoTx request frame.

In the embodiment of FIG. 9, when one of the APs participating in thecooperative transmit beamforming does not respond or one of CoTxresponse frames is lost, it may be difficult to determine a transmissionstart point in time of a beamformed data frame. To clarify thetransmission start point in time of the beamformed data frame, AP1leading the cooperative transmit beamforming may transmit a CoTx startframe. The CoTx start frame may be transmitted after a predeterminedtime interval is elapsed, when reception of a last CoTx response frameis completed. According to an embodiment, AP1 may transmit a beamformeddata frame to STA1 after a predetermined time interval is elapsed, whentransmission of the CoTx start frame is completed. AP2 and AP3 maytransmit beamformed data frames to STA2 and STA3, respectively, after apredetermined time interval is elapsed, when reception of the CoTx startframe is completed. Here, the predetermined time interval may be a SIFS.

FIG. 10 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.In FIG. 10, an AP associated with a first CoTx AP info field of a CoTxrequest frame may respond immediately after receiving the CoTx requestframe, and each of APs associated with remaining CoTx AP info fields ofthe CoTx request frame may respond after receiving a CoTx response pollframe.

Referring to FIG. 10, AP1, AP2, and AP3 may be determined to participatein the cooperative transmit beamforming through negotiation about thecooperative transmit beamforming. A cooperative sounding process for thecooperative transmit beamforming among AP1, AP2, and AP3 may beperformed. For example, each of AP1, AP2, and AP3 may acquire aprecoding matrix to be used for the cooperative transmit beamformingthrough the cooperative sounding process. AP1 leading the cooperativetransmit beamforming may transmit a CoTx request frame in which a BC isset as a receiver address. Here, a duration field of the CoTx requestframe is set as a time when a cooperative transmit beamforming durationis terminated and thus, a WLAN equipment unassociated with thenegotiation may set a NAV until the cooperative transmit beamformingduration is terminated. Also, a first CoTx AP info field of the CoTxrequest frame may include information indicating AP2 and a second CoTxAP info field of the CoTx request frame may include informationindicating AP3. Accordingly, AP2 and AP3 participating in thecooperative transmit beamforming may rest a NAV. AP2 associated with thefirst CoTx AP info field may transfer an ACK frame about the CoTxrequest frame to AP1 by transmitting a CoTx response frame in which AP1is set as a receiver address. Here, a duration field of the CoTxresponse frame is set as a time when the cooperative transmitbeamforming duration is terminated and thus, the WLAN equipmentunassociated with the negotiation may set a NAV until the cooperativetransmit beamforming duration is terminated. AP1 leading the cooperativetransmit beamforming may transmit a CoTx response poll frame in whichAP3 associated with a subsequent CoTx AP info field is set as a receiveraddress. AP3 receiving the CoTx response poll frame may transfer an ACKframe about the CoTx response poll frame to AP1 by transmitting a CoTxresponse frame in which AP1 is set as a receiver address. Here, aduration field of the CoTx response frame is set as a time when thecooperative transmit beamforming duration is terminated and thus, theWLAN equipment unassociated with the negotiation may set a NAV until thecooperative transmit beamforming duration is terminated. AP1, AP2, andAP3 may perform the cooperative transmit beamforming during thecooperative transmit beamforming duration. For example, AP1 may transmita beamformed data frame to STA1 belonging to a BSS covered by AP1, AP2,at the same time, may transmit a beamformed data frame to STA2 belongingto a BSS covered by AP2, and AP3, at the same time, may transmit abeamformed data frame to STA3 belonging to a BSS covered by AP3.According to an embodiment, AP1 and AP2 may transmit beamformed dataframes to STA1 and STA2, respectively, after a predetermined timeinterval is elapsed, when reception of a last CoTx response frame iscompleted. AP3 associated with a last CoTx AP info field may transmit abeamformed data frame to STA3 after a predetermined time interval iselapsed, when transmission of a CoTx response frame is completed. Here,the predetermined time interval may be a SIFS.

As described above, according to embodiments, the transmissionefficiency in an OBSS environment may be enhanced by providing acooperative transmit beamforming method that enables three or more APsto concurrently perform a transmit beamforming in the OBSS environment.

FIG. 11 illustrates an example in which BSSs covered by APs of a WLANoverlap. Referring to FIG. 11, a BSS 121 is covered by an AP 111 and aBSS 122 is covered by an AP 112. STAs 131 and 133 may belong to the BSS121, and STAs 132 and 134 may belong to the BSS 122. An overlapping areamay be present between the BSSs 121 and 122 of the APs 111 and 112. TheSTA 131 belonging to the BSS 121 and the STA 132 belonging to the BSS122 may be positioned in the overlapping area. Dissimilar to theembodiment of FIG. 1 or FIG. 7, the APs 111 and 112 are positionedoutside an OBSS area and the STAs 131 and 132 are positioned in the OBSSarea. In this environment, since a transmission start point in time of abeamformed data frame using direct communication between APs cannot beknown, an STA positioned in an OBSS area may be employed as a relayequipment.

FIG. 12 illustrates still another example of a protocol for performingcooperative transmit beamforming between APs according to an embodiment.FIG. 12 illustrates a method of using an STA positioned in an OBSS areabetween APs participating in the cooperative transmit beamforming as arelay equipment.

Referring to FIG. 12, AP1 and AP2 may be determined to participate inthe cooperative transmit beamforming through negotiation about thecooperative transmit beamforming. According to an embodiment, AP1 mayrecognize that AP1 and AP2 are positioned outside an OBSS area and STA1belonging to a BSS covered by AP1 is positioned in the OBSS area,through the negotiation. A cooperative sounding process for thecooperative transmit beamforming between AP1 and AP2 may be performed.For example, each of AP1 and AP2 may acquire a precoding matrix to beused for the cooperative transmit beamforming through the cooperativesounding process. AP1 leading the cooperative transmit beamforming maytransmit a CoTx request frame in which STA1 that is a relay equipment isset as a receiver address. Here, a duration field of the CoTx requestframe is set as a time when the cooperative transmit beamformingduration is terminated and thus, a WLAN equipment unassociated with thenegotiation may set a NAV until the cooperative transmit beamformingduration is terminated. STA1 receiving the CoTx request frame maytransmit a CoTx request frame in which a BC is set as a receiveraddress, so that AP2 may reset a NAV. AP2 receiving the CoTx requestframe may transfer an ACK frame about the CoTx request frame to STA1 bytransmitting the CoTx response frame in which STA1 is set as a receiveraddress. Here, a duration field of the CoTx response frame is set as atime when the cooperative transmit beamforming duration is terminatedand thus, the WLAN equipment unassociated with the negotiation may set aNAV until the cooperative transmit beamforming duration is terminated.STA1 may receive a CoTx response frame from APs participating in thecooperative transmit beamforming and then transmit a CoTx start frame.The CoTx start frame may be transmitted after a predetermined timeinterval is elapsed, when reception of a last CoTx response frame iscompleted. AP1 and AP2 may concurrently perform the cooperative transmitbeamforming during the cooperative transmit beamforming duration. Forexample, AP1 may transmit a beamformed data frame to STA1 belonging to aBSS covered by AP1 and, at the same time, AP2 may transmit a beamformeddata frame to STA2 belonging to a BSS covered by AP2. According to anembodiment, AP1 and AP2 may transmit beamformed data frames to STA1 andSTA2, respectively, after a predetermined time interval is elapsed, whenreception of a CoTx start frame is completed. Here, the predeterminedtime interval may be a SIFS.

As described above, according to embodiments, the transmissionefficiency in an OBSS environment may be enhanced by providing acooperative transmit beamforming protocol that enables two or more APsto concurrently perform transmit beamforming in the OBSS environment byusing an STA positioned in an OBSS area as a relay equipment when APshaving the OBSS area are positioned outside the OBSS area.

The units described herein may be implemented using hardware components,software components, or a combination thereof. For example, a processingdevice may be implemented using one or more general-purpose or specialpurpose computers, such as, for example, a processor, a controller andan arithmetic logic unit, a digital signal processor, a microcomputer, afield programmable array, a programmable logic unit, a microprocessor orany other device capable of responding to and executing instructions ina defined manner. The processing device may run an operating system (OS)and one or more software applications that run on the OS. The processingdevice also may access, store, manipulate, process, and create data inresponse to execution of the software. For purpose of simplicity, thedescription of a processing device is used as singular; however, oneskilled in the art will be appreciated that a processing device mayinclude multiple processing elements and multiple types of processingelements. For example, a processing device may include multipleprocessors or a processor and a controller. In addition, differentprocessing configurations are possible, such as parallel processors.

The software may include a computer program, a piece of code, aninstruction, or some combination thereof, for independently orcollectively instructing or configuring the processing device to operateas desired. Software and data may be embodied permanently or temporarilyin any type of machine, component, physical or virtual equipment,computer storage medium or device, or in a propagated signal wavecapable of providing instructions or data to or being interpreted by theprocessing device. The software also may be distributed over networkcoupled computer systems so that the software is stored and executed ina distributed fashion. In particular, the software and data may bestored by one or more computer readable recording mediums.

The above-described exemplary embodiments of the present invention maybe recorded in non-transitory computer-readable media including programinstructions to implement various operations embodied by a computer. Themedia may also include, alone or in combination with the programinstructions, data files, data structures, and the like. Examples ofnon-transitory computer-readable media include magnetic media such ashard disks, floppy disks, and magnetic tape; optical media such as CDROM disks and DVDs; magneto-optical media such as floptical disks; andhardware devices that are specially configured to store and performprogram instructions, such as read-only memory (ROM), random accessmemory (RAM), flash memory, and the like. Examples of programinstructions include both machine code, such as produced by a compiler,and files containing higher level code that may be executed by thecomputer using an interpreter. The described hardware devices may beconfigured to act as one or more software modules in order to performthe operations of the above-described exemplary embodiments of thepresent invention, or vice versa.

Although a few exemplary embodiments of the present invention have beenshown and described, the present invention is not limited to thedescribed exemplary embodiments. Instead, it would be appreciated bythose skilled in the art that changes may be made to these exemplaryembodiments without departing from the principles and spirit of theinvention, the scope of which is defined by the claims and theirequivalents.

What is claimed is:
 1. A communication device for performing cooperativebeamforming communication, the communication device comprising: atransceiver configured to transmit and receive a frame associated withnegotiation about a cooperative transmit beamforming with one or moreother communication devices having an overlapped basic service set(OBSS) area with the communication device, to transmit a cooperativetransmission request frame to the one or more other communicationdevices, and to receive a cooperative transmission response frame thatis transmitted from the one or more other communication devices inresponse to the cooperative transmission request frame; and a controllerconfigured to control the transceiver to perform the cooperativetransmit beamforming with the one or more other communication devices,upon a completion of reception of the cooperative transmission responseframe, during a time duration of the cooperative transmit beamformingand after a predetermined time interval has elapsed from the completionof the reception.
 2. The communication device of claim 1, wherein thecontroller is further configured to control the transceiver to transmitthe cooperative transmission request frame to the one or more othercommunication devices in response to the transceiver receiving the frameassociated with the negotiation from the one or more other communicationdevices.
 3. The communication device of claim 1, wherein the controlleris further configured to generate the cooperative transmission requestframe to be transmitted to the one or more other communication devices.4. The communication device of claim 1, wherein the cooperativetransmission request frame comprises a Cooperative Transmission(CoTx)control field which includes information on a number of communicationdevices that participates in the cooperative transmit beamforming. 5.The communication device of claim 1, wherein the cooperativetransmission request frame comprises Cooperation Transmission AccessPoints (CoTxAP) info fields which include information indicating thecommunication devices that participate in the cooperative transmitbeamforming.
 6. The communication device of claim 1, wherein a durationfield of the cooperative transmission request frame and a duration fieldof the cooperative transmission response frame are set as a time thatthe cooperative transmit beamforming duration terminates.
 7. Acommunication device for performing cooperative beamformingcommunication, the communication device comprising: a transceiverconfigured to transmit and receive a frame associated with negotiationabout a cooperative transmit beamforming with one or more othercommunication devices having an OBSS area with the communication device,to transmit a cooperative transmission response frame in response to acooperative transmission request frame that is transmitted from the oneor more other communication devices; and a controller configured tocontrol the transceiver to perform the cooperative transmit beamformingwith the one or more other communication devices, upon a completion ofreception of the cooperative transmission response frame by the one ormore other communication devices, during a time duration of thecooperative transmit beamforming and after a predetermined time intervalhas elapsed from the completion of the reception.
 8. The communicationdevice of claim 7, wherein the controller is further configured togenerate the cooperative transmission response frame to be transmittedto the one or more other communication devices.
 9. The communicationdevice of claim 7, wherein the cooperative transmission request framecomprises a Cooperative Transmission (CoTx) control field which includesinformation on a number of communication devices that participates inthe cooperative transmit beamforming.
 10. The communication device ofclaim 7, wherein the cooperative transmission request frame comprisesCooperative Transmission Access Points (CoTxAP) info fields whichinclude information indicating the communication devices thatparticipate in the cooperative transmit beamforming.
 11. Thecommunication device of claim 7, wherein a duration field of thecooperative transmission request frame and a duration field of thecooperative transmission response frame are set as a time that thecooperative transmit beamforming duration terminates.
 12. A relay devicefor performing cooperative beamforming communication, the relay devicecomprising: a transceiver configured to: receive a cooperativetransmission request frame that is transmitted from a communicationdevice, broadcast the cooperative transmission request frame, andreceive a cooperative transmission response frame that is transmittedfrom one or more other communication devices having an OBSS area withthe communication device to the communication device in response to thecooperative transmission request frame; and a controller configured tocontrol the transceiver to broadcast a cooperative transmission startframe in response to the cooperative transmission response frame so asto the communication device and the one or more other communicationdevices perform the cooperative transmit beamforming, upon a completionof reception of the cooperative transmission start frame, during a timeduration of the cooperative transmit beamforming and after apredetermined time interval has elapsed from the completion of thereception.
 13. The relay device of claim 12, wherein the cooperativetransmission request frame comprises a Cooperative Transmission(CoTx)control field which includes information on a number ofcommunication devices that participates in the cooperative transmitbeamforming.
 14. The relay device of claim 12, wherein the cooperativetransmission request frame comprises a Cooperative Transmission AccessPoints (CoTx AP) info fields which include information indicating thecommunication devices that participate in the cooperative transmitbeamforming.
 15. The relay device of claim 12, wherein a duration fieldof the cooperative transmission request frame and a duration field ofthe cooperative transmission response frame are set as a time that thecooperative transmit beamforming duration terminates.